1. Field of the Invention
This invention relates to apparatus for connecting and disconnecting joints of pipe, particularly pipe joints in a string of pipe in an offshore location, such as used for piling or as used for conductor casing on an offshore well.
2. Description of the Prior Art
In the drilling of offshore oil and gas wells it is necessary to sink large pipes into the subsea bottom, such pipes consisting of a number of joints of pipes connected together end to end. For example, such pipes may consist of a conductor casing which is drilled, driven or jetted into the sea floor a substantial distance, and which has connected to its upper end and extending upwardly to an above-water platform or floating vessel a conductor riser which constitutes a large diameter pipe through which drilling operations are performed.
In addition, the support legs of offshore plateforms from which drilling operations are performed often consist of pipe through which hollow steel pilings are driven or drilled into the sea bed.
Each of such pipes have been connected by various means in the past, including ordinary screw threads, welding, clamps, and a special type of breech block connection such as is shown, for example, in U.S. patent application Ser. No. 103,839, filed Jan. 4, 1971, which is assigned to the assignee of the present application.
In making up the aforesaid strings of pipe, a first joint of pipe is lowered from a platform or vessel and following joints of pipe are connected in sequence above it. As each connection is made, the string of pipe is lowered until it sinks down into the sea bottom and the drilling, driving or jetting operation is then performed to sink the string deeper into the sea bottom, with additional joints of pipe being added as necessary. Because of many advantages found therein, the breech block connector, as, for example, of the type described in the aforesaid patent application Ser. No. 103,839 has been found to be particularly advantageous. Such connections are made up at the surface and the connection is secured by a latch to prevent any possibility of the connection being released at an underwater or underground location. Examples of such breech block joints and latches thereon may be found, for example, in U.S. Pats. No. 3,421,580 and 3,442,536, and in U.S. application Ser. No. 387,667, filed Aug. 13, 1973 and assigned to the assignee of the present application.
In some instances it is necessary to disconnect a joint in a string of such pipe. For example, in the case of the conductor casing for an oil well, the conductor riser may be disconnected after the well is completed, since it is not needed thereafter. In the past it has been necessary to stop all operations on the platform and send a diver down to release the latch so that the joint may be disconnected. This has been a very undesirable and expensive practice, because no operations can be performed while the diver is under water, and the operation may take several hours in many cases. Furthermore, where the water is extremely deep or cold, there is a high current flowing, or the connection to be released is buried in the mud, it is difficult if not impossible for a diver to release it.
U.S. patent application Ser. No. 350,982, filed Apr. 13, 1973 and assigned to the assignee of the present application, such a connection having a latch which is remotely operable to disengage the connection. The latch shown there is resiliently biased in latching position, and a hydraulic cylinder is connected to the latch. Means are provided for applying hydraulic fluid under pressure to the hydraulic cylinder to release the latch. This apparatus is well suited to many applications, but suffers the disadvantage of requiring hydraulic lines to be run down the string of pipe to the joint which is to be disconnected. Because of the possibility of damage to the hydraulic system, it is necessary to provide an auxiliary manual means for releasing the latch.